The present invention is directed to di(C.sub.1 -C.sub.3)alkyl cis-N-(2-(phthalimido)ethyl)piperidine-2,5-dicarboxylate esters of the formula (II) below, and to processes which employ this compound as an intermediate in the conversion of a di(C.sub.1 -C.sub.3)alkyl cis-piperidine-2,5-dicarboxylate (of the formula (I) below) to a racemic (C.sub.1 -C.sub.3)alkyl (7S*,9aS*)-4,6,7,8,9,9a-hexahydro-2H,3H-pyrido[1,2-a]pyrazin-1-one-7-carbo xylate ester (of the formula (III) below). The structural diagrams and the R* and S* symbols employed herein are intended to designate relative, not absolute, stereochemistry.
Compounds of the formula (III) are known, having been previously described by Bright et al. as intermediates useful in the synthesis of certain bis-aza-bicyclic anxiolytic agents of the formula ##STR1## wherein X is N or CH and Y represents one of certain pyrazolo, triazolo, tetrazolo or cyclic imido radicals, in International Patent Application published under the Patent Cooperation Treaty (PCT), International Publication No. WO 90/08144, July, 1990.
Preparation of isomeric (C.sub.1 -C.sub.3)alkyl (7R*,9aS*)-4,6,7,8,9,9a-hexahydro-2H,3H-pyrrido[1,2-a]pyrazin-1-one-7-carb oxylate esters from di(Cl--C3)alkyl piperidine-2,5-dicarboxylate via analogous processes and intermediates is des concurrently filed U.S. Pat. Application 07/661,726 by Urban for "Process for trans-Piperidine-2,5-dicarboxylates."